The invention relates to an error current circuit breaker.
Error current circuit breakers are house wiring devices intended to protect people from dangerous electric shock and buildings from fires caused by electric wiring. Most of the error current circuit breakers in use today consist of a housing in which a totalizing or summing current transformer, a magnetic relay, a switch gear and a testing means (test key) are accommodated.
It is known that these devices may fail in the course of time. Thus the elements shown to be most vulnerable are the magnetic relay and the testing means. An essential feature of the magnetic relay of an error current circuit breaker is the very small gap between the pole surfaces of its armature and yoke. If after months or years of not being opened, these magnet contacts gradually cold-weld the finely ground pole surfaces, as is known to happen to relays, the response level of the error current citcuit breaker will gradually rise as well, until the weld (a diffusion welding process) is so firm that there is total adhesion of the armature to the yoke. Even in complete absence of permanent magnet flux, the spring action will then not suffice to release the armature, unlock the switch gear, and so interrupt the circuit.
Therefore error current circuit breakers are generally equipped with a test key to be operated manually. There is also a known error current circuit breaker with automatic testing (EP A 0,502,393).
Further, GB A 2,056,094 discloses a device for testing error current circuit breakers, not intended, however, for installation in the circuit breaker.
Most known earth-leakage circuit breakers currently operate independently of the mains voltage (see G. Biegelmeier: "Schutzmassnahmen in Niederspannungs- anlagen" Protective measures in low-voltage systems!; Osterreichischer Gewerbeverlag, Vienna, 1978), but there are also so-called DI circuit breakers, which are mains-dependent earth-leakage circuit breakers. Like circuit breakers independent of the mains voltage, the DI circuit breakers have a totalizing or summing current transformer with a secondary winding, which is connected to mains-dependent evaluation electronics. The advantage of these circuit breakers lies in the fact that they do not require any highly sensitive trip devices, such as the magnetic trip devices. The electronics can supply any desired insensitive relay, which, in the case of a leakage current, trips the switchgear. The switchgear can even be a contactor controlled by this electronics.
Furthermore, European Patent 0,220,408 describes a self-monitoring earth-leakage circuit breaker in which the regular operational test can be omitted, through the fact that the earth-leakage circuit breaker continuously monitors itself throughout the whole operating time. In addition, the earth-leakage circuit breaker also opens in case of interruption of the current supply and does not automatically close again when the current supply is resumed. In this case, the monitoring relates primarily to the electronic circuit. The circuit breaker opens when the rated non-operate current is exceeded. It is not in a position to detect an impending defect.
Earth-leakage circuit breakers with both a manually operable test key and an automatic test key according to German Patent 4,106,652, which, for example, check the mode of operation of the earth-leakage circuit breaker at monthly intervals, have the disadvantage that only a circuit breaker that is no longer tripping, i.e., a circuit breaker that is no longer performing the protective function, is detected. The result of this is that the protection does not exist for weeks, and even months, and the circuit breaker fails in an emergency during this period. Added to this is the fact that only the switching value of the leakage current is checked.
K. W. Brunner, in the journal Elektrische Maschinen 73, 10-12 (April 1994), writes that there are reasons for checking not only the switching values but also the response times for the leakage current. These lie, among other things, in the connection between the body current i.sub.b and flow time t in the case of contact with a current-conducting line. As already mentioned, Biegelmeier describes this relationship in detail. It also follows from Diagram 1, which shows the function I.sub..DELTA. =f(.DELTA.t).
The regions of action, shown in the diagram, of a 50/60 Hz alternating current on the human body, according to IEC Report 479, Chapter 2, Second Edition, are as follows:
Region 1 . . . As a rule, no reaction; PA1 Region 2 . . . As a rule, no pathophysiologically hazardous reaction; PA1 Region 3 . . . Transition region without fixed boundaries. As a rule, no organic damage; no danger of ventricular fibrillation, but muscular reactions and respiratory complaints with increasing current strength and duration of action; PA1 Region 4 . . . Increasing probability of ventricular fibrillation (curve c.sub.2 =probability below 5%, curve c.sub.3 =probability below 50%). With increasing current strength and duration of action, strong pathophysiological effects, such as cardiac arrest, respiratory arrest, and burns. With respect to ventricular fibrillation, the curves c.sub.1 through c.sub.3 relate to longitudinal flow from the left hand to the left foot. For durations of actions of less than 200 ms, ventricular fibrillation occurs only in the vulnerable phase, if the threshold values are exceeded. PA1 (1) They do not show a fail-safe behavior. PA1 (2) In case of failure of the electrical or electronic control unit, they can not always maintain the earth-leakage protection function. PA1 (3) They do not take into consideration the possibly flowing insulation currents, such as, for example, the capacitive leakage currents. PA1 (4) They do not monitor the main current contacts for welding and/or the switchgear for jamming or the like. PA1 (5) They do not check the opening of the contacts of the magnetic trip device. PA1 (6) They do not check the electronic control unit.
If the flow time, which is equal to the response time of an earth-leakage circuit breaker, has a value of, for example, 40 ms, then a leakage current of the order of magnitude of 100 to 200 mA, as a rule, does not show any pathophysiologically dangerous action. If, on the other hand, it has a value of .gtoreq.100 ms, then a leakage current of 100 to 200 mA would be risky for humans. If it were to have a value of .gtoreq.500 ms, then 30 mA would already be risky. It is recognized that the product of the leakage current and response time is of great importance.